Cancer claims millions of lives each year. On a world wide basis, cancer represents the single largest cause of death in both men and women. Cancer chemoprevention, a term coined by Sporn in 1976, can be defined as the prevention, inhibition, or reversal of carcinogenesis by administration of one ore more chemical entities, either as individual drugs or as naturally occurring constituents of the diet. Because carcinogenesis is a multistage process there is considerable opportunity for intervention and a number of potential targets for chemoprevention have recently been identified. Based upon the time period during which agents appear to exhibit activity in animal models of carcinogenesis, the major types of chemopreventive agents are: inhibitors of carcinogen formation, 'blocking agents' and 'suppressing agents'. Blocking agents, i.e. inhibitors of tumor initiation, can act by inhibition of carcinogen uptake, inhibition of formation or activation of carcinogen, deactivation or detoxification of carcinogen, preventing carcinogen binding to DNA, or enhancing the level of fidelity of DNA repair. Chemopreventive activity by antioxidant agents includes scavenging reactive electrophiles, scavenging oxygen radicals, and inhibiting arachidonic acid metabolism. Suppressing agents can be described more specifically as inhibitors of tumor promotion/progression. Antiproliferation/ antiprogression activities include, among others, modulation of hormonal and growth factor activity, induction of programmed cell death (apoptosis), and inhibition of angiogenesis. Many classes of natural products, having anti-oestrogenic, anti-inflammatory, antioxidative and/or anti-angiogenic activity, such as carotenoids, isothiocyanates, terpenoids, polyphenols, flavonoids, isoflavones, plant sterols, saponins, lignans and coumarins have shown a great deal of promise. The rationale for this research project is to search molecular evidence for chemopreventive activities shown by three medicinal plants and to link these activities with and establish structure activity relationships for their known and unknown constituents. The work will be focused on, but not limited to, types of constituents for which, based on previous reports, chemopreventive properties can reasonably be expected, but for which the mechanisms of action is mostly unknown.